#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <vector>

using namespace std;

int longestArithSeqLength(vector<int>& nums) {
    int n = nums.size();
    unordered_map<int, int> hash;
    hash[nums[0]] = 0;

    vector<vector<int>> dp(n + 1, vector<int>(n + 1, 2));

    int ret = 2;
    for (int i = 1; i < n; ++i)
    {
        for (int j = i + 1; j < n; ++j)
        {
            int a = 2 * nums[i] - nums[j];
            if (hash.count(a))
                dp[i][j] = dp[hash[a]][i] + 1;
            ret = max(ret, dp[i][j]);
        }
        hash[nums[i]] = i;
    }

    return ret;
}

int main()
{

	return 0;
}